1. Field of the Invention
The present invention relates generally to the field of Computer Automated Design (CAD) systems, particularly to graphic symbol storage and generation on CAD systems.
2. Description of Background Art
Graphic symbols are useful for characterizing the functionality of electronic devices. The American National Standards Institute (ANSI) and the Institute of Electrical and Electronic Engineers (IEEE) developed the ANSI/IEEE Standard 91-1984, hereafter "the standard," to guide design engineers in constructing graphic symbols for logic devices, hereafter "functional logic symbols."
Functional logic symbols accurately and concisely illustrate the logical functions of devices. The standard utilizes various features to illustrate the logical function of these devices. These features include pins, elements, and dependency notations. Pins denote electrical connections to the device. Each pin may be associated with one or more attributes that indicate the functions of the pin, e.g., a logic negation symbol. Elements are groups of pins and sub-elements that comprise a functional unit within the device, e.g., an AND-GATED device. Dependency notations are graphics, including text, that are used to describe detailed functional relationships between pins. A more detailed description of these features is given below.
One area where functional logic symbols are used is in the area of Electronic Design Automation (EDA). Engineers use EDA tools to design electrical circuits, e.g., an application specific integrated circuit (ASIC). When designing an electrical circuit, functional logic symbols are displayed on the computer monitor to represent the functional logic devices, e.g., a flip flop, within the circuit. Conventional EDA systems comprise a symbol library that contains functional logic symbols representing thousands of functional logic devices. Each functional logic device is uniquely represented by a functional logic symbol.
Generating and maintaining these symbol libraries is problematic. Conventional libraries are generated manually by a graphic symbol designer. Generating and maintaining a symbol library requires an annual investment of several person-years. In addition to the labor costs involved in generating and maintaining a symbol library, the library frequently contains errors and inconsistencies, e.g., pin spacing or pin ordering may differ for similar devices. Consistency is important when using the standard in order for an engineer to quickly and accurately discern the function of a device. Another problem with conventional systems is that significant memory is required to store the graphical representation for each function logic device.
It is therefore desirable to provide a system and method for quickly generating an accurate and consistent functional logic symbol while reducing the expense in generating and maintaining the symbol library and while reducing amount of memory necessary to store the symbol library.